From 48f170fb7d7db8789ccc23e051af61f62af5f685 Mon Sep 17 00:00:00 2001 From: Hugh Dickins Date: Mon, 25 Jul 2011 17:12:37 -0700 Subject: [PATCH] tmpfs: simplify unuse and writepage shmem_unuse_inode() and shmem_writepage() contain a little code to cope with pages inserted independently into the filecache, probably by a filesystem stacked on top of tmpfs, then fed to its ->readpage() or ->writepage(). Unionfs was indeed experimenting with working in that way three years ago, but I find no current examples: nowadays the stacking filesystems use vfs interfaces to the lower filesystem. It's now illegal: remove most of that code, adding some WARN_ON_ONCEs. Signed-off-by: Hugh Dickins Cc: Erez Zadok Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- mm/shmem.c | 50 ++++++++++++++++---------------------------------- 1 file changed, 16 insertions(+), 34 deletions(-) diff --git a/mm/shmem.c b/mm/shmem.c index bf6e9c11d859..7533574109da 100644 --- a/mm/shmem.c +++ b/mm/shmem.c @@ -972,20 +972,7 @@ static int shmem_unuse_inode(struct shmem_inode_info *info, swp_entry_t entry, s error = add_to_page_cache_locked(page, mapping, idx, GFP_NOWAIT); /* which does mem_cgroup_uncharge_cache_page on error */ - if (error == -EEXIST) { - struct page *filepage = find_get_page(mapping, idx); - error = 1; - if (filepage) { - /* - * There might be a more uptodate page coming down - * from a stacked writepage: forget our swappage if so. - */ - if (PageUptodate(filepage)) - error = 0; - page_cache_release(filepage); - } - } - if (!error) { + if (error != -ENOMEM) { delete_from_swap_cache(page); set_page_dirty(page); info->flags |= SHMEM_PAGEIN; @@ -1072,16 +1059,17 @@ static int shmem_writepage(struct page *page, struct writeback_control *wbc) /* * shmem_backing_dev_info's capabilities prevent regular writeback or * sync from ever calling shmem_writepage; but a stacking filesystem - * may use the ->writepage of its underlying filesystem, in which case + * might use ->writepage of its underlying filesystem, in which case * tmpfs should write out to swap only in response to memory pressure, - * and not for the writeback threads or sync. However, in those cases, - * we do still want to check if there's a redundant swappage to be - * discarded. + * and not for the writeback threads or sync. */ - if (wbc->for_reclaim) - swap = get_swap_page(); - else - swap.val = 0; + if (!wbc->for_reclaim) { + WARN_ON_ONCE(1); /* Still happens? Tell us about it! */ + goto redirty; + } + swap = get_swap_page(); + if (!swap.val) + goto redirty; /* * Add inode to shmem_unuse()'s list of swapped-out inodes, @@ -1092,15 +1080,12 @@ static int shmem_writepage(struct page *page, struct writeback_control *wbc) * we've taken the spinlock, because shmem_unuse_inode() will * prune a !swapped inode from the swaplist under both locks. */ - if (swap.val) { - mutex_lock(&shmem_swaplist_mutex); - if (list_empty(&info->swaplist)) - list_add_tail(&info->swaplist, &shmem_swaplist); - } + mutex_lock(&shmem_swaplist_mutex); + if (list_empty(&info->swaplist)) + list_add_tail(&info->swaplist, &shmem_swaplist); spin_lock(&info->lock); - if (swap.val) - mutex_unlock(&shmem_swaplist_mutex); + mutex_unlock(&shmem_swaplist_mutex); if (index >= info->next_index) { BUG_ON(!(info->flags & SHMEM_TRUNCATE)); @@ -1108,16 +1093,13 @@ static int shmem_writepage(struct page *page, struct writeback_control *wbc) } entry = shmem_swp_entry(info, index, NULL); if (entry->val) { - /* - * The more uptodate page coming down from a stacked - * writepage should replace our old swappage. - */ + WARN_ON_ONCE(1); /* Still happens? Tell us about it! */ free_swap_and_cache(*entry); shmem_swp_set(info, entry, 0); } shmem_recalc_inode(inode); - if (swap.val && add_to_swap_cache(page, swap, GFP_ATOMIC) == 0) { + if (add_to_swap_cache(page, swap, GFP_ATOMIC) == 0) { delete_from_page_cache(page); shmem_swp_set(info, entry, swap.val); shmem_swp_unmap(entry); -- GitLab